WL#10744: Full-Text Index Type

Support creation of Full-Text Index of a Sub-Document
Full-Text indexes allow searching the entire document (or a sub-document) for any
text value contained.
Full-Text search of JSON documents may require a custom fulltext parser and/or
additional querying extensions to be fully useful (e.g. json_textcontains() from
Oracle).

## External Requirements
A xprotocol client
X1
: MUST be able to create a FULLTEXT index on document of a collection
X2
: MUST be able to create a FULLTEXT index on a sub-document of a collection
X3
: MUST be able to optionally specify the name of a fulltext parser for a FULLTEXT index
X4
: MUST be able to specify the name of the index
X5
: MUST be able to specify if the (sub-)document has to exist
X6
: MUST be able to drop the index by name via the drop_index admin command.
X7
: MUST receive an Error message if the create_fulltext_index operation fails.
## Internal Requirements
The create_fulltext_index operation
F1
: MUST fail if generated ALTER TABLE statement fails like
* wrong fulltext parser
* names too long
* index with the same name exists
* generated column with the same name exists
F2
: MUST fail if a 'unique' FULLTEXT is requested